The present invention relates to projecting an image through use of a liquid crystal display device.
A conventional projector of this kind employs liquid crystal display panels 2a, 2b and 2c as shown in FIG. 1. The liquid crystal display panels are each an ordinary black-and-white active matrix liquid crystal display panel with no color filter, and each picture element serves as a light valve, that is, a switch which permits or inhibits the passage therethrough of light incident thereto.
Light 4 emanating from a light source 3, such as a halogen lamp, is converged by a reflector 5, passes through an infrared interference filter (a filter for intercepting or reflecting infrared rays) 6 and then enters a dichroic mirror 7B, by which blue light 4B contained in the light 4 is reflected to a direction perpendicular to the direction of incidence thereto, thereafter being reflected by a reflecting mirror 8 for incidence to the liquid crystal display panel 2c. Light having passed through the dichroic mirror 7B enters a dichroic mirror 7G, by which green light 4G is reflected to a direction perpendicular to the direction of incidence thereto for incidence to the liquid crystal display panel 2b. Light having passed through the dichroic mirror 7G is red light 4R, which is reflected by reflecting mirrors 9 and 10 one after the other for incidence to the liquid crystal display panel 2a.
On the other hand, there are displayed on the liquid crystal display panels 2a, 2b and 2c black-and-white images (or monochromatic images) corresponding to R (red), G (green) and B (blue) signals which are video signals. The red light 4R, the green light 4G and the blue light 4B pass through these liquid crystal display panels 2a, 2b and 2c, respectively, and enter a dichroic prism 11. These incident rays of light bear the images displayed on the liquid crystal display panels 2a, 2b and 2c and are combined by the dichroic prism 11 into one color image, which is projected by a projection lens 12 onto a screen 13 to create thereon an enlarged color image.
The conventional projector is of the type in which images displayed on respective liquid crystal display panels are combined and projected by the projection lens 12 onto a screen to create thereon an enlarged image. To solve problems of spherical and chromatic aberrations of the lens, the prior art device calls for a combination of many complicated lenses--this inevitably increases a loss of the quantity of light by them.
Further, it is difficult to enlarge the aperture of the projection lens 12, and the relatively small liquid crystal display panels 2a, 2b and 2c must be used in accordance with the diameter of the projection lens 12. For projecting an image on a wide screen it is necessary to increase the distance between the screen and the projector; in the former, a large space is needed, and in the latter, to enlarge the diameter of the lens 12 becomes more difficult.
Moreover, the prior art device requires three liquid crystal display panels and involves splitting light by the two dichroic mirrors 7B and 7G and then combining them by the dichroic prism 11. Hence, adjustment of the positions of the three liquid crystal display panels 2a, 2b and 2c is cumbersome and the device is complicated in structure and expensive.